1. Field of the Invention
The present invention relates to a receiver and a method therefor, and more particularly a receiver applicable, for example, to a terminal device for transmitting and receiving signal such as voice signal over a telecommunications network such as an IP (Internet protocol) network.
2. Description of the Background Art
In recent years, voice communication over an IP network, i.e. Voice over Internet Protocol (VoIP) network, has become widespread. In a VoIP network, each terminal device has its own operational clock system specifically provided thereto. Even though they are intended to have the same clock frequency, it would vanishingly be improbable that they coincide with each other, due to the operational clocks working specifically to the respective terminal devices. For this reason, there occurs difference in working speed, even a minute difference in operational clock frequency, between the terminal devices, which brings about excess or deficiency in received data in their receiver buffers when processing the received data.
In view of solving the problems described above, in Japanese patent laid-open publication No. 2003-46490 to Fushimi, et al., there is proposed a method for correcting excess or deficiency in the received data, i.e. a method for covering a difference in operational clock frequency, by adjusting a silent section of the received data in the buffer so as to delete a part of, or insert unvoiced data into, the silent section.
Further, in Japanese patent laid-open publication No. 272295/1999 to Sasaki, there is a proposed method for correcting excess or deficiency in received data, i.e. covering a difference in operational clock frequency, by controlling the receiver buffer in terms of a count of samples of the received data per predetermined length of time, i.e. sampling rate.
However, the method disclosed in Fushimi, et al., involves problems of degradation in sound quality, such as telephone speech quality, caused by erroneous decision on a voiced/unvoiced section or by fluctuation in the ratio of the length of voiced section to the length of unvoiced section.
Further, a method disclosed in Sasaki involves a problem of change in frequency components of received signals due to control over the sampling rate. For example, in the case that a voice signal is received from a speaker, change in the frequency components causes change in the sound quality, which might reproduce a different voice from the original voice of that speaker. Moreover, in the case that a sound signal other than voice signal is received, change in the frequency components causes change in the frequency that the sound originally has. The above-described problems are extremely significant.